Network Working Group Luca Martini Internet Draft Ali Sajassi Intended status: Standards Track Cisco Systems Inc. Expiration Date: November 2007 May 2007 802.1ah Ethernet Pseudowire draft-martini-pwe3-802.1ah-pw-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract An Ethernet Pseudowire (PW) is used to carry Ethernet/802.1ah frames over an MPLS network. This enables service providers to offer "emulated" Ethernet services over existing MPLS networks. This document specifies the encapsulation of 802.1ah Ethernet Frames Martini & Sajassi [Page 1] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 within a pseudo wire. It also specifies the procedures for using a PW to provide a "point-to-point Ethernet" service. Table of Contents 1 Specification of Requirements ........................ 2 2 Acronyms and Abbreviations ........................... 2 3 Introduction ......................................... 3 4 Applicability Statement .............................. 3 5 Ethernet 801.1ah I-tagged Tagged Mode encapsulation .. 4 6 Generic Encapsulation Procedures ..................... 5 6.1 The Control Word ..................................... 5 6.2 QoS Considerations ................................... 6 7 Intellectual Property Statement ...................... 7 8 Full Copyright Statement ............................. 8 9 IANA Considerations .................................. 8 10 Normative References ................................. 8 11 Author Information ................................... 9 1. Specification of Requirements The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. 2. Acronyms and Abbreviations * Service Instance TAG (I-TAG): A 4-byte tag identified by its own Ethertype value defined in IEEE 802.1ah. * Service Instance Identifier (I-SID): A field of the Service Instance TAG which identifies the service instance within an 802.1ah domain. Martini & Sajassi [Page 2] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 3. Introduction A new Ethernet Pseudowire (PW) is used to carry 802.1ah Ethernet [AH] frames over an Multi Protocol Label Switched [RFC3031] network. In addressing the issues associated with carrying an 802.1ah Ethernet frame over a Public Switched Network (PSN), this document assumes that a Pseudowire (PW) has been set up by using a control protocol such as the one as described in [RFC4447]. The design of Ethernet Pseudowire described in this document conforms to the pseudo wire architecture described in [RFC3985]. It is also assumed in the remainder of this document that the reader is familiar with RFC3985 and [RFC4448]. Two distinct types of Ethernet PW are described in [RFC4448]: a raw mode Ethernet PW (PW type 5) and a 802.1Q tagged mode Ethernet PW (PW type 4). This documents describes a method to encapsulate 802.1ah tagged frames into MPLS which will be called a 801.1ah I-tagged Ethernet PW. 4. Applicability Statement The Ethernet PW emulation allows a service provider to offer a "I-SID to I-SID" Ethernet based service across an MPLS packet switched network (PSN). In keeping with the PW architecture, we wish to minimize the processing work needed to forward the packet along the PW. One important point is to use the MPLS label as the demultiplexer to determine where the Ethernet packet needs to be forwarded at the egress PE. For this reason a PW of type 5 (Raw Ethernet) is not suitable for this application as it would use the I-SID as the demultiplexer/service delimiter, and not the MPLS PW label. The 801.1ah I-tagged Ethernet PW has the following characteristics in relationship to the respective native service: - Ethernet 801.1ah I-tagged PW connects two Ethernet I-Sid aware forwarders, supporting bi-directional transport of variable length Ethernet frames. The ingress Native Service Processing (NSP) function strips the preamble and FCS from the Ethernet frame and transports the frame in its entirety across the PW. The egress NSP function receives the Ethernet frame from the PW and regenerates the preamble and FCS before forwarding the frame to the attachment circuit. Since FCS is not being transported across the PW, payload integrity transparency may be lost. The OPTIONAL methods described in [RFC4720] can be used to achieve payload integrity transparency on Ethernet 801.1ah I-tagged PWs. Martini & Sajassi [Page 3] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 - I-tag rewrite can be achieved by NSP at the egress PE which is outside the scope of this document. - The 801.1ah I-tagged Ethernet PW only supports homogeneous Ethernet frame type across the PW; both ends of the PW must I- tagged. Heterogeneous frame type support achieved with NSP functionality is outside the scope of this document. - 801.1ah I-tagged Ethernet status notification is provided using the PW Status TLV in the LDP status notification message. Loss of connectivity between PEs can be detected by the LDP session closing, or by using [VCCV] mechanisms. The PE can convey these indications back to its attached Remote System. - The maximum frame size that can be supported is limited by the PSN MTU minus the MPLS header size, unless fragmentation and reassembly is used [RFC4623]. - The packet switched network may reorder, duplicate, or silently drop packets. Sequencing MAY be enabled in the 801.1ah I-tagged Ethernet PW to detect lost, duplicate, or out-of-order packets on a per-PW basis. - The faithfulness of an 801.1ah I-tagged Ethernet PW may be increased by leveraging Quality of Service features of the PEs and the underlying PSN. (see "QoS Considerations" section) 5. Ethernet 801.1ah I-tagged Tagged Mode encapsulation The Ethernet frame will be encapsulated according to the procedures defined later in this document. If the PE detects a failure on the Ethernet physical port, or the port is administratively disabled, it MUST send PW status notification message for all PWs associated with the port. If the PE is notified that the I-SID has been removed , or is in a down state it MUST notify the egress PE using the PW status procedures defined in [RFC4448]. The method by which the PE learns that the I-SID in no longer in service is outside the scope of this document. This mode uses service-delimiting I-tags to map input Ethernet frames to respective PWs and it corresponds to PW type 0x001F "Ethernet I- Tagged Mode". [Note: Pending IANA allocation] Martini & Sajassi [Page 4] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 6. Generic Encapsulation Procedures When the NSP/Forwarder hands a frame to the PW termination function: - The preamble (if any) and FCS are stripped off. - The control word as defined in the "The Control Word" section is, if necessary, prepended to the resulting frame. The conditions under which the control word is or is not used are specified below. - The proper Pseudowire demultiplexor (PW Label) is prepended to the resulting packet. - The proper tunnel encapsulation is prepended to the resulting packet. - The packet is transmitted. The way in which the proper tunnel encapsulation and pseudo wire demultiplexor are chosen depends on the procedures that were used to set up the pseudo wire. The tunnel encapsulation depends on how the MPLS PSN is setup. This can include no label, one or more labels. The proper pseudo wire demultiplexor is an MPLS label whose value is determined by the PW setup and maintenance protocols. When a packet arrives over a PW the tunnel encapsulation, if still present, is stripped off. Then the PW demultiplexor MPLS label is used to determine how to process the packet, no other information from the packet is required. If the control word is present, it is processed and stripped off. If needed, the I-SID in the I-tag is re- written according to a provisioned value. The resulting frame is then handed to the appropriate Forwarder/NSP. Regeneration of the FCS is considered to be an NSP responsibility. 6.1. The Control Word When carrying Ethernet over an MPLS backbone, sequentiality may need to be preserved. The OPTIONAL control word along the guidelines of [RFC4385] is defined here, and addresses this requirement. Implementations MUST support sending no control word, and MAY support sending a control word. If the control word is not used all the functionality defined in [RFC4385] is not available. In particular the PW packet may be mistakenly recognized as an IP packet by PSN devices that use the first nibble in the packet to identify it's Martini & Sajassi [Page 5] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 content. This problem is only significant if the PSN contain equal cost load sharing links that use the first nibble in the packet to identify it's content, and a destination MAC address starting with 0x4 or 0x6 as it first byte is used. In the case of the I-tag PW, it would be sufficient to void using the prefix 0x4 or 0x6 in the provider mac address space. A PW carried over an MPLS PSN that uses the contents of the MPLS payload to select the ECMP path SHOULD employ the PW MPLS Control Word, if strict packet ordering is required. In all cases the egress router must be aware of whether the ingress router will send a control word over a specific virtual circuit. This may be achieved by configuration of the routers, or by signaling, as defined in [RFC4447]. The control word is defined as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0| Reserved | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ In the above diagram the first 4 bits MUST be set to 0 to indicate PW data. The rest of the first 16 bits are reserved for future use. They MUST be set to 0 when transmitting, and MUST be ignored upon receipt. The next 16 bits provide a sequence number that can be used to guarantee ordered frame delivery. The processing of the sequence number field is OPTIONAL. The sequence number space is a 16 bit, unsigned circular space. The sequence number value 0 is used to indicate that the sequence number check algorithm is not used. The sequence number processing algorithm is found in [RFC4385]. 6.2. QoS Considerations The ingress PE MAY consider the 802.1ah Service Instance Drop Eligible (I-DEI) Indicator and of the Service Instance Priority Code Point (I-PCP) I-tag header when determining the value to be placed in a QoS field of the encapsulating protocol (e.g., the EXP fields of the MPLS label stack). In a similar way, the egress PE MAY consider the QoS field of the MPLS (e.g., the EXP fields of the MPLS label stack) protocol when queuing the frame for CE-bound. Martini & Sajassi [Page 6] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 A PE MUST support the ability to carry the Ethernet PW as a best effort service over the MPLS PSN. The 802.1ah bits are kept transparent between PE devices, regardless of the QoS support of the PSN. A PE may support additional QoS support by means of one or more of the following methods: -i. One COS per PW End Service (PWES), mapped to a single COS PW at the PSN. -ii. Multiple COS per PWES mapped to a single PW with multiple COS at the PSN. The PW guaranteed rate at the MPLS PSN level is PW service provider policy based on agreement with the customer, and may be different from the Ethernet physical port rate. 7. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Martini & Sajassi [Page 7] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 8. Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 9. IANA Considerations This document uses a new PW type. IANA already maintains a registry of name: "MPLS Pseudowire Types Registry" defined by RFC4446. The following value is suggested for assignment: PW type Description Reference ------- ----------------------------------------------- --------- 0x001F Ethernet 802.1ah I-Tagged Mode TBD 10. Normative References [AH] IEEE 802.1, "IEEE P802.1ah/D3.4 - Virtual Bridged Local Area Networks Amendment 6: Provider Backbone Bridges", March 10, 2007. [RFC3031] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label Switching Architecture", RFC3031, January 2001 [RFC3985] Bryant, et al., "PWE3 Architecture", RFC3985, March 2005. [RFC4447] "Transport of Layer 2 Frames Over MPLS", Martini, L., et al., rfc4447 April 2006. [RFC4448] L. Martini, Et. al "Encapsulation Methods for Transport of Ethernet over MPLS Networks", RFC4448, April 2006 [RFC4385] "PWE3 Control Word for use over an MPLS PSN", S. Bryant, G. Swallow, L. Martini, D. McPherson, RFC4385, Martini & Sajassi [Page 8] Internet Draft draft-martini-pwe3-802.1ah-pw-00.txt May 2007 February 2006 [VCCV] Nadeau, T., et al., "Pseudo Wire Virtual Circuit Connection Verification (VCCV)", Work in Progress, October 2005. [RFC4720] A. Malis, D. Allan, N. Del Regno, "Pseudowire Emulation Edge-to-Edge (PWE3) Frame Check Sequence Retention", RFC4720, November 2006 [RFC4623] Malis, A. and M. Townsley, "Pseudowire Emulation Edge-to- Edge (PWE3) Fragmentation and Reassembly", RFC 4623, August 2006. 11. Author Information Luca Martini Cisco Systems, Inc. 9155 East Nichols Avenue, Suite 400 Englewood, CO, 80112 e-mail: lmartini@cisco.com Ali Sajassi Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 e-mail: sajassi@cisco.com Martini & Sajassi [Page 9]